Data from: Different modes of migration among Late Cretaceous ammonoids in northwestern Hokkaido, Japan: evidence from the analyses of shell whorls

The thickness ratios of shell whorls (= whorl breadth / shell diameter) in
the ammonoids Damesites sugata, Hypophylloceras subramosum, and
Gaudryceras tenuiliratum from the Late Cretaceous outer shelf deposits in
the Kotanbetsu area of northwestern Hokkaido, Japan, were examined in
order to determine their mode of migration. The thickness ratios of D.
sugata differ significantly with depth on the outer shelf environment, but
show no significant difference laterally at a similar depth. These results
suggest that D. sugata did not frequently migrate to different depths on
the outer shelf environment, but tended to live and migrate laterally at a
similar depth on the outer shelf. The thickness ratios of H. subramosum
and G. tenuiliratum show no significant difference between different
depths on the outer shelf environment nor for lateral direction at a
similar depth. This suggests that H. subramosum and G. tenuiliratum
frequently migrated at different depths on the out er shelf environment
and laterally at a similar depth. There is no difference in hatchling
diameters in all the examined species at different depths on the outer
shelf environment, suggesting that the thickness ratios became manifest
after the post-hatchling stage due to limited migration, which would have
been in a nektobenthic habitat. The various modes of migration in the
study area are reconstructed in this study, suggesting a diversified
paleoecology of Late Cretaceous ammonoids.